Considerations for a Turntable

[Desertdweller]

A while back, someone posted here about the possibility of using a turntable with E-Z Track.  Of course, this is possible if you  substitute conventionally-supported rail between the E-Z Track and the turntable bridge.

This got me to thinking of considerations when choosing and installing a turntable.

My own model railroad uses two turntables.  These were purchased and installed in 2009, and are my only experience with turntables.

My turntables are made by Atlas.  The Bachmann turntables closely resemble these outwardly, but I do not know anything about the Bachmann tables beyond that.

Both brands are a surface mount type.  They do not require a hole in the layout, as there is no pit.  The mechanism is thin and is no taller than normal track and roadbed.  The rotating part of the turntable is completely covered over.  This is prototypical, but not typical of full-size turntables.  Fully decked turntables were used in places that received great amounts of snowfall.

The power system is contained in a small shed.  The Atlas model is powered by a large can-type motor.
In earlier model Atlas tables, power is transmitted from the motor to the drive mechanism by a rubber drive belt.  Later versions use a gear train for this.  Both my tables use the belt drive, and I have found this to be satisfactory. If you buy just the basic turntable, it will not come with a drive unit.  Instead, you get a hand crank.  Drive units are sold separately.

The table is turned by a Zurich mechanism turned by a worm.   The mechanism itself is too complicated for me to describe how it works, but what it does is convert a constant rotating force to an intermittent rotating force.  This causes the turntable bridge to stop intermittently at repeating equally-spaced positions.  Automatic indexing!

Full-size railroad turntables do not work this way.  Their movement is continuous and indexing is done by eye, with special locking devices.  Model turntables that do that require rotary switches, or a complex electric eye system to sense table position.  The Zurich mechanism is a cheap and easy way to avoid this.

Since this table uses fixed track locations, it is important that any roundhouse used with it has compatible stall spacing.  This is easily achieved by using a roundhouse marketed for use with that turntable.

Again, because of the fixed track locations, it is easiest to build the approach track first, then adjust the position of the table so the approach track can be perfectly straight.  You do not want a curve in the track in the final engine length before the table.  The whisker tracks coming off the table also need to be straight for at least the first engine length.

You cannot run E-Z Track all the way to the bridge.  The roundhouse is designed so the stall tracks will be at the correct height.  The whisker and approach tracks will need to be made with sectional regular or flex track, with cork or foam roadbed to support it.

Both vertical and horizontal rail alignment where meeting the bridge is critical.  On my approach track, I drilled a hole between ties and used a small wood screw to adjust vertical adjustment of the approach rails.

The turntable base should be securely screwed to the layout base.  There are holes cast into the base for this purpose.  It is important the turntable base be both stable and level.

Power to the bridge should be fed to the table from the approach track.  Each of the other tracks coming off the table should be controlled independently, using their own lead wires.

Power is fed from the base to the bridge via a split-ring contact system.  This automatically reverses the polarity of the bridge tracks after they had turned 180 degrees.  I found this to be confusing at first, and bought and installed an Atlas Controller for each turntable.  I didn't need these.  Only if you do not have polarity reversing built in would you need this, but it may be handy if you choose to power your turntable drive with the same power supply you are using to power your trains.

I had some problem with the power supply running to the bridge.  Each rail on the bridge has its own sliding, spring-loaded contact that presses against the contact plates in the base.  These contacts each consist of two tiny brass cups with a spring inside.  Sometimes these can get hung up and create a dead spot.

This can be cured by replacing the springs inside the cups with stronger springs.  I substituted coupler springs from the old N-scale Rapido couplers, stretched a little.  If you disassemble the turntable, be careful!
There are a lot of tiny parts in there!

Of course, these turntables will look lots better when painted.  I painted the "cement" base parts, and weathered the wooden deck.  The little sheds can be used to establish railroad identity.  Paint them in colors that are standard for the railroad they are being used on.  Add additional details: fuel tanks, barrels, people.

My tables get a lot of use, especially the one at my Burlington roundhouse.  They can be used for turning cars as well as locos, and give a little extra action to any model railroad.

Les

[skipgear]

Bachmann doesn't make an N-scale turntable. You are thinking of the new HO turntable which is a straight copy of the Atlas turntable.

[Desertdweller]

Tony,

That's right.  The Bachmann turntable is a copy of the Atlas HO turntable.  The Atlas N-scale turntable is a scaled-down copy of the Atlas HO turntable.  I should have made that clear.

Given the relationship between the turntable geometry and the roundhouse geometry, maybe we will see a Bachmann roundhouse.  Maybe even both in N scale.

There is not much that could be done to the Bachmann turntable to make it look different than the Atlas table.  Maybe a bridge truss structure atop the deck, or a different-looking shed.

But a roundhouse to go with the turntable would offer lots of opportunity for a distinctive model.  Only the track spacing would need to stay the same.  At a minimum, it could be molded with yellow or brown brick instead of red.

I painted the brick walls, the window frames, and doors of mine a dark red to more closely resemble the C&S-AT&SF Rice Yard roundhouse in Denver.  This is gone now, it is the location of the Elitch Gardens Amusement Park.  I glued the stall doors open and weathered the roof.  Then I added a matching brick annex to be the boiler house.

The other turntable wound up behind the Burnham Shops.  I have one track that continues through one of the Diesel shops and feeds the turntable.  On the prototype, the turntable was kept after the roundhouse was torn down, and was then used for turning locomotives around.  I have no whisker tracks off this table.
The shed was painted yellow with brown trim to reinforce the D&RGW appearance.

Les

[Jerrys HO]

Les

A while back, someone posted here about the possibility of using a turntable with E-Z Track.

This may be me you are thinking of. I have the HO tt and modified a Heljan roundhouse to use with the tt.

http://www.bachmanntrains.com/home-usa/board/index.php/topic,17942.0.html

I have done a little more with it but had to put aside as I am adding a 12ft. yard with a main loop at the end with the tt in the middle of the loop.

I do plan on redoing the roundhouse to accept longer approaches.

Jerry

[Desertdweller]

Something you also keep in mind is that the turntable under discussion here has a bridge only 100 scale feet long.  This is enough to hold two F-units, barely.  It will not hold two E-units, or even two PA units.

If you want to park a longer loco, you will need to install one extended-length whisker track directly opposite the approach track.  Then you can just run your loco across the table and onto the long track.  But you won't be able to turn it.  You will have to turn it on a reverse loop or wye.  If you want to store it in the roundhouse, you can extend the length of that stall.

I can think of at least one full-sized precedent for this.  When the CB&Q railroad decided to use articulated steam locomotives on its branch to Deadwood, SD, they were too long for the roundhouse there.  They extended a stall and named it "the Mallet Shed".

Les

[Bucksco]

Our HO turntable is NOT a copy of anyone's product. It is new tooling.

[Desertdweller]

Yardmaster:

I'm glad to hear that.  Will we see an N-scale version?  A roundhouse too?

Les

[Bucksco]

Anything is possible....

[skipgear]

Our HO turntable is NOT a copy of anyone's product. It is new tooling.

Sorry,
I stand corrected. It uses the same style drive mechanism as the Atlas but it is an inch longer, comes with the drive motor and control, and has 16 stalls vs. Atlas 22 stalls.  It looks to have a little bit of a pit vs. the Atlas which is a flat deck. With the stall spacing it will be very diffcult to find a roundhouse that will work. The Thomas roundhouse is pretty generic and should be sold seprately for those that don't want the manual turntable.

Back to N scale.

[railtwister]

Since the drive mechanism of the Bachmann turntable takes up the equivalent of two track spaces, the angle of the approach tracks should be about 20 degrees apart. The newer Atlas turntable has  tracks spaced at 15 degrees, so their roundhouse wouldn't work with the Bachmann turntable without some serious modification. Scratch building a roundhouse is not that difficult, I made one about 17 years ago to work with one of the original Atlas turntables that had a wider spacing than those available today, although I don't remember what that spacing actually was. I took the easy route and used sheet styrene to model what would have been a concrete block w/stucco structure, since the quantity of brick patterned styrene sheets needed for the project was beyond my budget. I used some styrene recycled from an old Evergreen Styrene counter-top rack discarded by my LHS when they switched to a larger floor-standing rack. Thin plywood, like doorskin, or matte board, such as task board would have been my next choice, but since the styrene was free, it was a no-brainer. Besides, styrene's not adversely affected by the high humidity we have in South Florida, like wood or cardboard would be.

Bill in FL

[Desertdweller]

It is sounding to me like it would be easier to scratchbuild a roundhouse than to try to modify a roundhouse that has stall spacing incompatible to the turntable.

I've scratchbuilt some fairly large buildings in N-scale.  I think I would tackle a scratchbuilt roundhouse by drawing the plan of the building full-size on a large sheet of paper.  Lay the turntable directly on the paper and trace the outline of the edge of it, then mark the track centers at the indexed positions and extend them out as radiuses to mark the stall centers and angles.  If your drawing is accurate, you could construct the roundhouse directly on this plan.

I don't recall seeing any roundhouses whose walls were actually round.  The outer back walls are a series of chords that are at right angles to the stall tracks.  While there may well be some that were curved, straight end walls would be easier to repair if an engine overshot the stall.

Les